Stable Wearable Strain Sensors on Textiles by Direct Laser Writing of Graphene

Strain sensors for smart wearable textiles have recently attracted great attention due to their potential in the healthcare applications, specifically, functions to track heartbeat, pulse signals, and movements of limbs and joints. Traditional methods typically require complicated procedures including dip-coating in different solutions to prepare sensing fibers before weaving into fabrics. In this study, we used an ultraviolet picosecond laser to directly induce graphene on polyimide (PI) fabric to produce a strain sensor. The process is mask-free, easy-to-fabricate, and the graphene tracks are well-adhered to the substrate. High-quality 3D-porous graphene was produced directly using appropriate laser parameters with a sheet resistance as low as 20 Omega/sq. The graphene strain sensors showed high sensitivity within a small strain range (strain below 4%) (GF(max) = 27), good linearity, a low threshold value (strain = 0.08%), and high stability (4% resistance loss after 1000 cycles). Furthermore, reliable signals gathered from various human motions demonstrated the potential for health-care monitoring.